An apparatus for enabling a liquid or dye to be conveyed from a nib of a source of liquid or dye to a fluid absorbent nib of a marker pen. The apparatus includes a tubular docking member having the source and the nib of the source at a first end and an open portion at a second end configured to receive and engage an end of the marker pen including the nib of the marker pen, the length of the docking member being such as to enable the nib of the marker pen selectively to be placed in contact with the nib of the source to cause liquid or dye to pass between the nib of the source and the nib of the marker pen. The liquid may comprise a translucent liquid such as water and the dye may comprise an indicator such as a water-based ink containing colored dyes, dispersed pigments or other coloring media.